1. Field of the Invention
The present invention relates generally to a dual seal mechanical connection. More specifically, the present invention relates to a mechanical pipe connection system for use in rigorous marine environments under both internal and external pressure and a method for its implementation.
2. Description of the Prior Art
The development of the petrochemical industry has emphasized the need for means to transport oil, gas and other fluids over considerable distances and often under rigorous conditions. The means to transport such fluids most often have taken the form of marine or terrestrial pipelines that link virtually all petrochemical production sites with refining and distribution facilities. Generally these pipelines are comprised of identical pipe segments that are welded end-to-end in an abutting relationship. Such welded pipelines, tend to be expensive to construct, and considerable testing must be undertaken to evaluate the integrity of the welded pipe joint. Moreover, this evaluation process must be continuously repeated over the life of the pipeline.
In addition to being able to withstand internal pressurization, marine flow lines, for example, must be able to withstand the high external pressures associated with placement along the seabed. As a consequence, exotic, high strength materials such as titanium have been used for such applications. Materials such as titanium, however, are very difficult to weld using conventional welding techniques. More conventional heat treated metals are also inappropriate for such applications, since welding destroys the strengthening property of the heat treated pipe section.
In addition to welded pipelines, a variety of mechanically coupled pipelines have been proposed. These mechanically joined pipelines are usually constructed of flanges or clamps that result in large diameter joint segments that can not be used easily in J-tubes. Mechanical pipe joints utilizing conventional threaded connections are often prone to loosen over a period of time, thereby rendering their use suspect for marine applications.
There exists a variety of seals or gaskets that are used to seal between flanges or other types of connectors. Such prior art seals may be generally categorized as those sealing elements that seal on the bore of the connector and those elements that seal on the face of the connector. In both categories, sealing usually is achieved by crushing or yielding (plastically deforming) the gasket; by elastically loading a flexible gasket utilizing a soft coating or plating on the seal surface; or by a combination of the two. These seals may or may not be pressure energized as dictated by their relative geometry and location in the connector.
Because of their relatively massive cross sections, some bore seals require considerably more bolt-up loading then do face seals. Alternatively, bore seals may be more economical due to lower manufacturing tolerances. Additionally, many or most bore seals are self centering, whereas face seals are generally extremely sensitive to misalignment. Flexible bore seals are particularly adaptable to high temperature use because they are radically compressed during make-up, resulting in residual seal loading.
Some prior art bore seals include a design having a flange portion oppositely disposed flexible lips and a centrally disposed rib portion. The lips of the seal are provided with annular sealing surfaces which taper outwardly toward the rib portion. Disadvantages, however, exist in the manufacture of such a design. While this type of seal is basically a bore seal, it incorporates some of the characteristics of a face seal, due to the presence of the rib portion which is normally disposed between the end faces of the connectors with which it is used. As a result, such a design requires higher manufacturing tolerances and is therefore more expensive to manufacture.
One solution to this problem was posed by Latham, as disclosed in U.S. Pat. No. 4,214,763. Latham discloses a flexible annular bore seal for sealing between first and second coaxially aligned members. In Latham, each of the first and second coaxially aligned members are provided with an internal frusto-conical sealing surface tapering inwardly toward the adjoining ends.
The present invention is directed to an improved mechanical connection for joining two conduits or pipes in fluid tight engagement. The present invention comprises a dual seal that provides fluid tight engagement against internal as well as external pressure.